We are proposing to develop a single, bench-top animal scanner that will acquire both functional SPECT images and anatomical CT images with sub-millimeter spatial resolution for both imaging modalities. The sub-mm SPECT-CT will provide a technique for noninvasive functional imaging in mice for a wide range of applications, including the development of new radio-pharmaceuticals, assessment of new therapeutic approaches, and investigation of fundamental biological processes in transgenic and knockout mice. This would allow investigators to perform serial imaging studies in the same animal at multiple time points to investigate tumor growth, tissue pathology, the effects of therapy, and the mechanism of action of new diagnostic agents. The system will have wide applicability and significant impact in research that uses small animals to advance our understanding of human disease processes. During phase I we successfully completed all proposed feasibility studies to demonstrate SPECT/CT with gamma performance of 1.3mm intrinsic spatial resolution, E range from 30keV to 350keV, and,deltaE/E=12% at 140keV and - 100mu m CT capability from a 50xS0mm CMOS based digital x-ray detector. In addition, we acquired outstanding dual SPECT-CT images of euthanized mice. During the phase II project we will complete the integration of the high-resolution SPECT and transmission CT subsystems and develop all necessary hardware and software. The result will be a fully functional dual-modality prototype scanner for anatomical and quantitative metabolic imaging of small animals.